For some time my research has been about neutrinos, and particularly about their mass. When I was at Los Alamos, our group developed a new type of tritium beta decay experiment using a source of gaseous molecular tritium, and we were able to push down the laboratory limits on the mass of the electron neutrino to below 10 eV, ruling out a claim that it was around 30 eV. In 1988 I joined the Sudbury Neutrino Observatory, and in 2001 SNO was able to show that electron neutrinos are actually mixtures of at least two mass eigenstates. Super-Kamiokande had shown that muon neutrinos also mix, and thus at least two of the three neutrino states have non-zero mass. SNO also resolved the "solar neutrino problem" and confirmed the astrophysical calculations of the flux of solar neutrinos.